I like that idea, and were I a Michigan resident, would probably select that option, but I would like to correct one historical misunderstanding the blogger known as the Great Orange Satan has:
In 1972, Republican voters in Michigan decided to make a little mischief, crossing over to vote in the open Democratic primary and voting for segregationist Democrat George Wallace, seriously embarrassing the state's Democrats. In fact, a third of the voters (PDF) in the Democratic primary were Republican crossover votes. In 1988, Republican voters again crossed over, helping Jesse Jackson win the Democratic primary, helping rack up big margins for Jackson in Republican precincts. (Michigan Republicans can clearly be counted on to practice the worst of racial politics.)In fact, both Wallace and Jackson would have won the Democratic contests in Michigan quite easily even without Republican support; Wallace was shot and nearly killed in the early morning of primary day, 1972, and received a large sympathy vote both there and in Maryland. His margin of victory was 23% over his next-closest rival, George McGovern, who also received significant Republican support that day. Jackson's triumph in the 1988 caucus was even more overwhelming, and while GOP mischief may have broadened the final margin, it was by no means the determining factor. If Romney is going to pull it out here, he's going to need more than liberals behind him.